The present invention relates to improvements in fuel dispensers to permit compensation of the measured amount of fuel dispensed to compensate for temperature fluctuations. As is known from elementary physics, the volume of most objects is dependent on temperature, with most things expanding when heated and contracting when cooled. This is true of liquid fuels like gasoline.
Since liquid fuels are typically sold by a volumetric measure, such as U.S. gallons, Imperial gallons, or liters, the mass of fuel sold in, for example, a U.S. gallon at 30 degrees Fahrenheit will differ from the mass sold at 90 degrees Fahrenheit. Since the actual fuel value will be dependent on the mass, the fuel value of the transaction is temperature dependent. Various governmental bodies with oversight over commercial weights and measures have from time to time required this to be taken into account, as reported in U.S. Pat. No. 4,101,056 to Mattimoe, the entire disclosure of which is incorporated herein by reference. However, this is a problem that has not been addressed to provide a commercially viable, temperature-compensating fuel dispenser. The issue is to make the amount sold by volume be normalized to a standard temperature, so that, for example, even at 30 degrees F., the fuel value sold as a gallon is the same as a 60 degree gallon.
One of the problems encountered is the problem of taking an accurate temperature. Obviously, there are a number of factors that affect the temperature of fuel, including the ambient temperature, prior ambient temperatures, insulation of the fuel from the ambient, possible heating by the pumping of the fuel, and the like. Also, the temperature must be taken on a real time basis, since there can be inhomogeneities in the temperatures of stored fuel, so that the actual temperature of the fuel may vary during a fueling transaction. Finally, the fact that the product involved is highly flammable must be taken into consideration. Any sparking or arcing in electronic components used to take the temperature could be disastrous.
The requirement to accurately sense temperature at several temperatures in a hazardous location imposes several constraints. Since the temperature sensors are in the vicinity of the gasoline, the sensors must either be intrinsically safe or explosion-proof to meet requirements of safety agencies. The problems with an explosion-proof system are cost of conduit or mineral insulation cable, difficulty in handling during installation, and finding space to locate an explosion-proof box. Explosion-proof items are generally very large and heavy. Multiple explosion-proof sensors further complicates a congested hydraulic area, and would be very difficult to retrofit.
The temperature readings require a high degree of accuracy and stability to maintain Weights and Measures authorities' approvals. As a result, it is valuable to have a system which provides temperature measurements with minimal error for an indefinite time period. The electronic and mechanical components will drift with time and temperature, causing associated drifts in temperature readings. While this could by compensated with trim settings and other calibrations for gain and zero adjustments, these can be misadjusted, can also change over time, and require time, tools and equipment to adjust.
Accordingly there is a need in the art for a precise, trouble-free, reliable, verifiable dispenser that corrects volume readings to compensate for temperature fluctuations.